A necessary precondition for the understanding of visual system pathology is that the normal visual system be understood in sme detail. A quantitative description of the retina at the level of single cells is likely to be the cornerstone for this broader understanding. Over the last two years may colleagues and I have made progress towards such a quantitative description of the first stages of visual processing in the salamander retina. This proposal continues the same basic strategy. By selectively destroying receptors in an isolated retina viewed under the microscope, I plan to isolate either one, or a pair of receptors from the neighbors to which they would otherwise be electrically coupled. This experimental simplification will allow me to examine in detail the properties of the connections between individual receptors. A second part of this proposal sets out to use simultaneous microelectrode impalement of cones and bipolar cells to establish the spatial extent and fine structure of bipolar cell receptive fields. Bipolar cell responses to small currents injected into receptors should also allow a preliminary analysis of the physiology of the receptor to bipolar cell synapse.